948 women in Skopje, Yugoslavia, whose first pregnancies were either carried to term or terminated by legal abortions were followed historically through record search and interview for an average of four years. The following research questions are addressed, using the information gathered: (a) Does the length of interval between an induced abortion and a subsequent pregnancy affect the outcome of the pregnancy/ (b) Is there evidence of a prolonged non-contracepting inter-pregnancy interval (suggesting reduced fecundity) following an induced abortion? (c) Is there evidence of an intervening "personality" factor in that women who first resort to induced abortion after their first delivery and before their second delivery have experienced a different first-delivery prematurity rate than have women who do not resort to an inter-birth induced abortion? (d) What factors differentiate non-aborters from (1) pre-marital aborters, (2) interbirth aborters, and (3) post-family-building aborters? (e) What factors differentiate (1) from (2) and (2) from (3) ? (f) What is the relationship between the level of effective contraception and incidence of induced abortion in a society desiring small families? (g) What effect on abortion incidence would the introduction of contraception post-abortion have? (h) What are the relationships of smoking before and after the pregnancy to birth weight as compared with smoking during pregnancy and with nonsmoking mothers? The methodology of applying stochastic models to epidemiologic problems will be further developed through use of existing techniques to test the current Markov Chain model for stationarity, Markovity, and homogeneity of data within subgroups and through development and testing of a Semi-Markov model to determine its effect on data reduction, model fit, and ease of generalization. Data were collected with Grant #719-0023, Ford and Rockefeller Foundations Program in support of Social Science and Legal Research on Population Policy. The Markov Chain model was developed under NIH Grant #HDO7214-02.